Heretofore, it has been demonstrated that the display of the decoded blue color signal on a color monitor, but cutting off the green and red beam currents of the display device, gives a display which is quite sensitive to distortions of the chrominance signal in National Television System Committee, hereinafter referred to as NTSC, and Phase Alternation Line, hereinafter referred to as PAL, color systems, and especially when those signals are recorded on, say, video tape recorders. The sensitivity of the "blue only" display is due, of course, to the formation of the NTSC and
video signals where the gain required of the demodulated blue minus luminance (B-Y) signal is 2.03, while that of the demodulated red minus luminance (R-Y) signal is 1.14, and that required of demodulated green minus luminance (G-Y) is less than unity.
The high gain afforded the decoded B-Y chrominance signal makes this particular signal the most sensitive to chrominance noise and distortions, green being the least sensitive. Thus, the blue only display is inherently more sensitive to noise than a display in full color due to the fact that with all three chrominance signals applied to the appropriate electron guns of the display device, along with the luminance signal, the constant luminance principle is observed, which tends to reduce the visibility of random noise in the NTSC and PAL systems. (For those desiring a further explanation of the constant luminance principle, see W. F. Bailey, "The Constant Luminance Principle in NTSC Color Television," Proceedings of the I.R.E., January, 1954, Volume 42, No. 1, Pages 60-66.)
However, in displaying the blue only signal, using the blue electron gun of the color picture tube, the brightness and visual acuity of the display leave much to be desired. Indeed, the human eyes' sensitivity to the standard blue color is low, the blue electron gun of the display device contributing but approximately eleven percent of the total luminance. However, by applying the "blue only" video signal to all of the electron guns of a typical three gun color picture monitor or display device, the resultant display can be very much brighter monochrome display. As the human eye has much better acuity to green than blue, the monochrome display is of increased sharpness as perceived by the human eye. Of course, in some color picture tubes, the design optimizes the spot size of the green electron beam because of the property of human vision.
Additionally, when observing human skin tones on the color picture monitor, operating so as to provide a monochrome picture composed of the decoded blue signal luminance plus blue minus luminance i.e., [Y + (B-Y)], these skin tones will appear somewhat darker grey than if only the luminance signal feeds the display device. That is, the B-Y signal is in the direction so as to reduce brightness when human skin tones are transmitted. This is because skin tones generate a chrominance signal at approximately one hundred three degrees (103.degree.) relative to the B-Y axis, namely, the +I phase (In NTSC the color difference or chrominance signals are transmitted with a restricted bandwidth and these signals are transformed to other signals called I and Q signals before they are bandwidth restricted.), or nearly so.
Correspondingly, an improvement in the basic technique of displaying the "blue only" signal would be to matrix R-Y and B-Y signals to form +Q signal which being in phase quadrature to +I, would not darken flesh tone grey scale reproductions. Such a matrix operation is possible either by synchronously demodulating the chrominance signal along the Q axis (33.degree. phase shift) or by matrixing decoded R-Y and B-Y signals in correct proportion.
As the displayed picture is in monochrome because all three electron guns are driven with the decoded blue signal, or Y+Q signal, it follows that it is possible to use a monochrome display device and drive it, the display device, with decoded blue signal or Y+Q. Here is provided essentially the same highly effective display of chrominance noise and distortion whereby a much simpler and less costly display device which affords economic advantages may be utilized.